Predistortion amplifier system with separately controllable amplifiers

Abstract

A wideband predistortion system compensates for a nonlinear amplifier's frequency and time dependent AM-AM and AM-PM distortion characteristics. The system comprises a data structure in which each element stores a set of compensation parameters (preferably including FIR filter coefficients) for predistorting the wideband input transmission signal. The parameter sets are preferably indexed within the data structure according to multiple signal characteristics, such as instantaneous amplitude and integrated signal envelope, each of which corresponds to a respective dimension of the data structure. To predistort the input transmission signal, an addressing circuit digitally generates a set of data structure indices from the input transmission signal, and the indexed set of compensation parameters is loaded into a compensation circuit which digitally predistorts the input transmission signal. This process of loading new compensation parameters into the compensation circuit is preferably repeated every sample instant, so that the predistortion function varies from sample-to-sample. The sets of compensation parameters are generated periodically and written to the data structure by an adaptive processing component that performs a non-real-time analysis of amplifier input and output signals. The adaptive processing component also implements various system identification processes for measuring the characteristics of the power amplifier and generating initial sets of filter coefficients. In an antenna array embodiment, a single adaptive processing component generates the compensation parameters sets for each of multiple amplification chains on a time-shared basis. In an embodiment in which the amplification chain includes multiple nonlinear amplifiers that can be individually controlled (e.g., turned ON and OFF) to conserve power, the data structure separately stores compensation parameter sets for each operating state of the amplification chain.

What is claimed is:  
     
       1. An amplifier system, comprising: 
       a data structure that stores sets of compensation parameters;  
       a compensation circuit coupled to an input to the amplifier system, wherein the compensation circuit digitally predistorts an input transmission signal, using sets of compensation parameters selected from the data structure;  
       an amplification chain coupled to an output of the compensation circuit, the amplification chain comprising a power splitter that divides the input transmission signal, following predistortion and radio frequency (RF) upconversion, into a plurality of RF component signals that are amplified by a plurality of respective nonlinear amplifiers and then combined for transmission; and  
       a control module that selectively adjusts states of individual amplifiers of the plurality of nonlinear amplifiers in response to variations in traffic conditions to conserve power during relatively low traffic conditions, such that the amplification chain has multiple operating states in which each operating state corresponds to a particular combination of nonlinear amplifier states;  
       wherein the data structure stores compensation parameter sets separately for each of the multiple operating states of the amplification chain, and the compensation module selects sets of compensation parameters from the data structure for use within the compensation circuit based in part on a current operating state of the amplification chain, such that the input transmission signal is predistorted according to the current operating state.  
     
     
       2. The amplifier system as in  claim 1 , wherein the control module selectively switches the individual nonlinear amplifiers between on and off states. 
     
     
       3. The amplifier system as in  claim 2 , wherein the control module additionally selectively adjusts the nonlinear amplifiers to intermediate operating points. 
     
     
       4. The amplifier system as in  claim 1 , wherein the control module controls each nonlinear amplifier using direct bias and power supply control lines. 
     
     
       5. The amplifier system as in  claim 1 , wherein, for each of the multiple operating states of the amplification chain, the data structure stores sets of compensation parameters that are indexed and selected for use based at least in-part on multiple characteristics of the input transmission signal. 
     
     
       6. The amplifier system as in  claim 5 , wherein the multiple characteristics include (1) an amplitude or power of the input transmission signal, and (2) an integrated envelope of the input transmission signal. 
     
     
       7. The amplifier system as in  claim 5 , wherein each set of compensation parameters comprises a set of finite impulse response filter coefficients. 
     
     
       8. A method of controlling an amplifier system, the amplifier system comprising an amplification chain having a power splitter that divides an input transmission signal into a plurality of RF component signals that are amplified by a plurality of respective nonlinear amplifiers and then combined for transmission, the method comprising: 
       selectively adjusting states of individual amplifiers of the plurality of nonlinear amplifiers, in response to variations in traffic conditions, to conserve power during relatively low traffic conditions, such that the amplification chain has multiple operating states in which each operating state corresponds to a particular combination of nonlinear amplifier states; and  
       selecting a set of compensation parameters from a data structure based in-part on the current operating state of the amplification chain, and loading the set of compensation parameters into a compensation circuit that predistorts the input transmission signal prior to application to the amplification chain, whereby a predistortion method applied by the compensation circuit to the input transmission signal depends upon the current operating state.  
     
     
       9. The method as in  claim 8 , wherein selectively adjusting the states of the individual amplifiers comprises selectively switching the individual nonlinear amplifiers between on and off states. 
     
     
       10. The method as in  claim 9 , wherein selectively adjusting the states of the individual amplifiers further comprises adjusting the nonlinear amplifiers to intermediate operating points. 
     
     
       11. The method as in  claim 8 , wherein selectively adjusting the states of the individual amplifiers comprises controlling each nonlinear amplifier using direct bias and power supply control lines. 
     
     
       12. The method as in  claim 8 , wherein, for each of the multiple operating states of the amplification chain, the data structure stores multiple sets of compensation parameters that are indexed and selected for use based at least in-part on multiple characteristics of the input transmission signal, and wherein selecting a set of compensation parameters from the data structure further comprises measuring the multiple characteristics of the input signal to generate indices to the data structure. 
     
     
       13. The method as in  claim 12 , wherein the multiple characteristics include (1) an amplitude or power of the input transmission signal, and (2) an integrated envelope of the input transmission signal. 
     
     
       14. The method as in  claim 8 , wherein the set of compensation parameters comprises a set of finite impulse response filter coefficients for predistorting the input transmission signal. 
     
     
       15. The method as in  claim 8 , wherein the input transmission signal is a wideband signal.